The invention relates to a process for manufacturing pasteurized substrates.
In a known process of appropriate generic form, following preparation in the usual manner by processes of sifting, separation and size reduction, refuse is introduced into a circular fermentation container with a circular motion of distribution at the perimeter and, for the purpose of introducing and maintaining an aerobic and biological process of decomposition, the refuse is constantly agitated and gradually displaced towards the central exit aperture of the fermentation container. The refuse is agitated by a sequence of connected movements running in a screw-like motion in a predetermined circular direction. This process prevents the so-called "short circuit currents" in the refuse material, where parts of the refuse to be treated reach the exit aperture in a shorter time than the residence time required for complete biological decomposition or conversion respectively of the refuse material. Thus an attempt is made to avoid mixing the already fermented final product with refuse which has not yet decomposed.
From this suggestion concerning the process in question, no exact details can be gathered about the total length of time needed for the process. On the basis of appropriate reference to the corresponding publication, it is highly probable that the residence time of the waste to be treated in the fermentation container will be, perhaps, between 4 and 6 days. Further, this suggestion does not state whether there is a periodic process procedure in which a definite amount of refuse is put into the fermentation container each time and then fermented or whether it is a matter of a continuously supplied and running decomposition process.
Finally, the suggestion does not offer any advice as to the composition of the refuse to be processed: whether and to what extent agricultural waste, sewage sludge, liquid manure etc., can be processed using this method. Only urban refuse is mentioned as a raw material to be treated. Furthermore, the question of sterilizing the final product remains open.
In accordance with the statement, the process in question is simply an intensive aeration of the refuse material by continuous agitation of same, while it is transported from the inlet of the fermentation container to the outlet of same in an unspecified residence time.
There is a known composting device which has a swivel bridge which traverses the associated circular fermentation container along the diameter of same and which can move along the rails secured in circular fashion around the upper edge of the container by means of rollers attached to both ends of the swivel bridge. The swivel bridge can be driven with the aid of an electric drive via a step-down gear acting on one of the rollers. In this way it is also supported by a central bearing which is attached to the truncated cone shaped inner wall in the centre of the inside of the fermentation container. Further the swivel bridge consists of two bridge halves which each go from the central bearing radially to the perimeters of the container. One of the bridge halves bears a screw conveyer which is assigned to convey the waste material to be processed to the periphery of the fermentation container. This extends from a receiving funnel assigned to the central bearing to a delivery chute situated in the peripheral area. On the other half of the bridge, numerous motor-driven aerating screws are attached in two parallel rows, which run radially between the truncated cone shaped inner wall and the cylindrical outer wall of the fermentation container. The points of the aerating screws are set in a downwards direction from the bridge and are inclined diagonally so that each spiral tip points forwards in the direction of rotation of the bridge and at the same time in the direction of the outer wall of the container. In addition, the aerating screws in one row are displaced in a radial direction with regard to those in the other row. The screw surface of the aerating screws lifts the refuse material from the base of the container and, stirring continuously, transports it upwards.
The fermentation container can be filled between 80 and 85% of the height of the wall.
The rotation of the bridge is supported by the aerating screws which rotate in the same direction and intimately mix the refuse across the whole width of the fermentation container. The air necessary for the said process is supplied by means of a ventilator, via a number of openings near the base of the outer wall and via the distribution pipes connecting the openings with the ventilator.
The treated refuse material can be expected to displace itself in a continual and uniform movement from the outer wall to the exit in the inner wall as a result of the diagonal position of the aerating screws.
The peripheral speed of the individual aerating screws can be set to achieve a suitable decomposition of the refuse material. There are also measures to suspend the operating of the device in case an aerating screw comes into contact with an unexpected obstacle.
A number of power operated probes, which can be inserted into the fermentation container from below, help to achieve the prevailing conditions of, for example, temperature and oxygen content of the refuse being treated and to control the supply of air.
A major disadvantage of the equipment as described previously is its cost of construction. There is also the drawback of the considerable amount of energy required and the numerous opportunities for error.